I had this after I drove over a bumper (transit van crashed out on a motorway) the bumper smacked the fuel tank and the vibration locked the FSU up. I went over a few potholes and shook it loose and it was fine again.

Try taking it over a bumpy trek a few times and that should shake it loose.

This happened to me the other day, exactly the same way, I set off in third gear and it stalled, I turned the key and the fuel needle was registering nothing, the computer said zero miles left and the fuel light was lit.........quarter of a tank of fuel left at least!

I stopped and restarted 3 times with no avail,so started driving home and after 7 miles everything slowly returned to normal!

Yeah the problem with the FSU is its one of the few "truly mechanical" parts that are left on modern cars. Like a float in a toilet basin, it behaves the same and if it gets stuck it can read all sorts of weird results...